Newtonsoft.json: Support freezing a JToken

[sharwell]

I'd like to propose the ability to "freeze" a JToken. A frozen JToken is essentially read-only; any attempt to change one of its properties results in an InvalidOperationException.

• The term "a JToken" refers to any instance of a class derived from JToken.
• When a JToken is initially created, it is not frozen.
• When a JToken is frozen, all children of the JToken are frozen as well.

No changes would be made to any current public API.

I would be happy to implement this functionality and send a pull request if you like the idea.

[JamesNK]

This is a little easier now that there is JsonLoadSettings. Could add a flag to that that loaded tokens should be frozen.

[BalassaMarton]

Any news on this? I just stumbled into a problem which I could solve nicely with immutable JObjects

[Avivskie]

Any update with this one?